The present invention relates to an internal combustion engine piston and connecting rod assembly which can extend a stroke of a piston in a cylinder body of limited height.
The height of a cylinder body of a conventional internal combustion engine is determined according to a dimension p between a crown surface of a piston and an axis of a piston pin, a length l of a connecting rod connected to the piston and a crank arm of a crank shaft (a distance between an axis of the piston pin and an axis b of a axial portion of the arm of the crank shaft), and a length r of the arm of the crank shaft. Accordingly, an increase in displacement in a conventional or existing multicylinder internal combustion engine can be obtained by either increasing the bore of the cylinder or increasing the stroke 2r of the piston.
According to the first method, the thickness of the wall between the cylinders adjacent to each other is reduced, and there is a limit to the increase of displacement. In the aforementioned second method, the position of the piston pin with respect to the piston is moved upwardly to shorten the dimension p, whereby the arm of the crank shaft is lengthened by that amount. However, in the existing multicylinder internal combustion engine, there is scarcely present allowance in the dimension p between the crown surface of the piston and the piston pin (see Japanese Utility Model Application Laid-open No. 64-47958). When the dimension p is shortened, a combustion chamber becomes so shallow that the shape of the combustion chamber is restricted, making it difficult to obtain a satisfactory combustion condition.
In view of the foregoing, the height h of the cylinder body or the dimension p of the piston is not actually changed but the connecting rod is shortened to lengthen the arm of the crank shaft by that amount. However, when the length l of the connecting rod is shortened and the length r of the arm of the crank shaft is lengthened (that is, l/r is decreased), piston slap becomes noticeable, resulting in abrasion of the piston ring, increase in slap noise and a reduction in fuel efficiency.
However, in order to effectively control the emission of exhaust gases in the future, an increase in displacement of cylinders of the existing engine is required. The problem then is how to increase displacement without changing the height of the cylinder body in an internal combustion engine.
The object of the present invention, therefore, is to provide a piston and connecting rod coupling which can effectively increase a stroke of a piston without changing the height of a cylinder body.